The Furnace Cold Air Return Vents

October 13, 2009


About this time every year, my blog gets a lot of traffic from people searching for “can I cover my cold air return vents?”

Answer: no.

I want to address this issue again. If you have a forced air furnace, realize that there is an exchange of air going on with it– cold air to hot air. Your furnace needs to take in cold air, heat it up, and blow it out through your heater vents as heated air. If you cover your cold air return vents, you are starving your furnace, creating an air vacuum in your home (leading to an uncomfortable atmosphere), and perhaps filling your home with trace amounts of carbon monoxide.

Do not cover your cold air return vents.

I did a post about this when I renovated my living room, and re-did some of the furnace ducting to the room. I had done some studying and talked with my furnace guy. You can read the post here. You can also read my recent post about changing your furnace filters— it’s an easy chore. Not changing dirty filters can damage your furnace and wind up costing you more money on your heating bills, too.


Now, my home has cold air return vents, but not enough. Not only do you need vents, you need a proper amount for proper air exchange. My house, at about 1680 square feet, only has two small cold air return vents– for the entire house! That is far too few. My Furnace Guy said that for every heater vent (and size) in a room, there should be a cold air return vent. Bedrooms almost never have them, and this explains why bedrooms are so cold in the winter– there is no full air exchange but rather a vacuum of air. The heated air really has nowhere to go, since there is no air flow; and the room air remains stagnant and chilly. So ideally, every room should have a cold air return vent (or at least larger ones in key areas of the home). I know! This sounds awful, because with duct work, you have to rip out walls and work with metal. It’s NOT fun. However, the next time you have a wall open or if you decide to build an addition to your home, keep these things in mind. Your furnace will appreciate it, and it will show in the heating bills.

And in the meantime, keep all those cold air return vents uncovered!

Photos courtesy of Americanhvacparts and Office of Energy Efficiency of Canada.

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